1. Field of the Invention
This invention relates to the use of gyrotropic material such as ferrites to construct devices having high angular sensitivity to microwave radiation by virtue of the directivity inherent in the relation for the refractive index of an electro-magnetic wave propagated in a gyrotropic medium.
2. Prior Art
A gyrotropic medium is one whose properties are isotropic in the absence of a magnetic field, but which exhibits anisotropy, i.e. quantitative differences in measurements of the same properties along different crystal axes, when such a field is applied. This characteristic arises in ferrite materials as a consequence of the effect of the field on the electron spin component of the magnetic moment of the atomic lattice, and is the basis of the non-reciprocal properties which are extensively used in ferrite circulators and isolators and many other waveguide and microstrip circuit elements at microwave frequencies.
The continual decrease in size, and increase in power and sensitivity, of solid state transmitters and receivers in the microwave frequency band now makes the relatively large size of the antenna structure required in many microwave systems an inconvenient anomaly. While devices using the well-established techniques of phased arrays and aperture synthesis may be utilised to reduce structure dimensions, a lower limit remains which is essentially determined by the wave length of the radiation and the dimensions of the radiating aperture.